Use the information below to answer the questions that follow. Enter your answers using digits only $-$ no dollar signs, commas, or decimal points. The business's year$-$end is December $31.$

Cost of equipment $=105000$

Useful life in years $=3$

Residual value $=15000$

Date purchased $=$ January $31$

$1.$ What is the depreciation expense per year?

$2.$ What is the depreciation expense per month?

$3.$ What is the depreciation expense in the year of purchase?